Human beings balance one's body while standing by almost always positioning oneself by refined body movements (referred to as fluctuation of the center of gravity). Conventionally, a test has been conducted to check fluctuation of the center of gravity by using a stabilometer to find how much a body fluctuates based on the measured result. The stabilometer measures fluctuation of the center of gravity when a body is on the stabilometer.
Moreover, conventionally, there has been a technique to estimate fluctuation of the center of gravity by using an acceleration sensor. According to the technique, a position at a measurement is obtained by applying a double integration to an acceleration value measured by the acceleration sensor to estimate a fluctuation of the center of gravity. When a double integration is applied to an acceleration value, an integration constant such as an initial position and an initial speed is provided. However, according to the technique, a calculation is conducted by assuming an initial position and an initial speed as 0. In other words, in the technique, a measurement is assumed to be started under a standstill state.
Related-art techniques are disclosed in WO2004/014230, Japanese Laid-open Patent Publication Nos. 2008-229266 and 2008-073267.